The present invention relates to an art of manufacturing filter cigarettes of a type designed to take air into a filter through small holes in a tip-paper piece to thereby achieve a desired dilution characteristic, and especially to a filter cigarette air permeability characteristic stabilization device for stabilizing the ratio of the amount of the air which flows into a filter through small holes in a tip-paper piece.
The taste of a filter cigarette of this type depends on its dilution characteristic, and the dilution characteristic depends much on the amount of air taken in, especially taken in through a filter. Specifically, the higher the degree of dilution, the milder the cigarette tastes. Conversely, the lower the degree of dilution, the stronger the cigarette tastes. Hence, in order to ensure that manufactured filter cigarettes (products) have stable quality, it is required to stabilize the ratio of the amount of the air which flows through a filter to the amount of the air which flows through an entire filter cigarette (this ratio will be hereinafter referred to as xe2x80x9cair-flow ratioxe2x80x9d).
One of the causes of difference in air-flow ratio between products is difference in space between the circumference of a filter-tip and a tip-paper piece (hereinafter, this difference will sometimes be referred to as xe2x80x9cdifference in circumferential tip spacexe2x80x9d). Thus, there is found large difference in circumferential tip space, among all manufactured products. Specifically, when a tip-paper piece is rolled around the circumference of a filter-tip more tightly, the space between the circumference of the filter-tip and the tip-paper piece is smaller. Hence, air-flow resistance in small holes is larger, and accordingly, the ratio of the air flowing into the filter is lower. Conversely, when a tip-paper piece is rolled around the circumference of a filter-tip less tightly, the space between the circumference of the filter-tip and the tip-paper piece is larger. Hence, air-flow resistance in small holes is smaller, and accordingly, it can be said that the air-flow ratio tends to be higher.
In this connection, for example, Japanese Patent Unexamined Publication No. H5-268928, Japanese Utility Model Examined Publication No. H7-45200 etc. disclose a technique in which, when a tip-paper piece is rolled around a cigarette and filter-plug in a filter attachment machine, rolling of the tip-paper piece is performed following rotation of the cigarette and filter-plug stably, to thereby prevent inappropriate rolling of the tip-paper piece. It is recognized that, in the technique known from those publications, glue on the tip-paper piece is preliminarily dried prior to rolling of the tip-paper piece, to enhance the initial adhesive power of the glue to thereby help stable rolling of the tip-paper piece.
However, paper like tip-paper has a material property such that, when it is dried, fibers shrink as the water content thereof decreases. Here, the larger the reduction in water content of paper, the larger the fiber shrinkage tends to be. In manufacturing filter cigarettes, if the water content of a tip-paper web as a material is not uniform, tip-paper pieces, which are cut from the tip-paper web, shrink to different degrees of shrinkage (at different shrinkage percentages) when glue on them is dried after they are rolled around half-finished filter cigarettes, respectively. The difference in shrinkage percentage between tip-paper pieces leads to difference in the above-mentioned circumferential tip space between products, and hence difference in air-flow resistance in small holes. Thus, in manufacturing filter cigarettes, the ratio of the air flowing into a filter cannot be stabilized perfectly, only by preventing inappropriate rolling of a tip-paper piece.
In this connection, it is conceivable, in manufacturing filter cigarettes, to keep rolls of tip-paper web as a material under control so that they may have the same water content all the time, to thereby keep the percentage of shrinkage caused by glue-drying within a certain range. However, in paper factories, printing factories and tobacco-manufacturing factories, conditions such as humidity, temperature, etc. under which tip-paper webs are stored are different. In addition, the water content of a tip-paper web varies depending on countries and regions of the world, and are much affected by external factors such as seasons, change in weather, etc. in different regions and countries. Thus, it is technically very difficult to keep all rolls of tip-paper web as materials in the same water-content condition, under normal environmental conditions of existing factories.
The present invention has been made in order to achieve many objects. One of the objects is to make it possible to manufacture high-quality filter cigarettes, without adding large-scale new equipment.
One mode of an apparatus for stabilizing air permeability characteristic of filter cigarettes according to the present invention can be carried out, for example, by modifying filter cigarette manufacturing equipment. Specifically, it is designed to dry a tip-paper web forcibly in the process of supplying the tip-paper web to a rolling section of a filter attachment machine, to thereby stabilize the water content of a tip-paper piece, which is to be rolled around a cigarette and filter-plug, in an absolute dry region. It is however to be noted that the present invention is not restricted to a mode achieved by modifying cigarette manufacturing equipment. It may be of a mode such that all the structure is built separately anew.
As stated above, the water content of a web as a material varies depending on environmental conditions. The normal range of water content is defined depending on environmental conditions of a country or region where filter cigarettes are to be manufactured. For example, in Japan, normally, the water content of a web is, on average, in a region of about 4% and above, throughout the year. It can be said that also in other countries and regions, the water content of a web is lower, for example, in dry climate, and higher in humid climate.
As stated above, the range of water content of a web varies as environmental conditions vary. However, it can be said that the water content of a web has a lower limit which depends on the environmental conditions of a country or region. The present invention intends to eliminate the influence of difference in water content of a web (material) upon manufactured filter cigarettes (products), by preliminarily drying the web to thereby lower, in advance, the range of water content of the web into an absolute dry region, which is a lower water-content region as compared with a normal water-content region.
For example, in a filter attachment machine suited for high-speed operation, a double-length cigarette received from a cigarette making machine is divided in two, and a filter-plug of twice the length of a filter-tip is arranged between those two cigarettes in the manner that the two cigarettes and the filter-plug are in line, to thereby form a half-finished double-filter cigarette. The half-finished product is supplied to a rolling drum in a rolling section. While the half-finished double-filter cigarette as a whole rolls on the rolling drum, a tip-paper piece is rolled around the half-finished double-filter cigarette, to thereby form a double-filter cigarette. A tip-paper web is drawn out continuously from a roll. While the web is guided along a feed path, glue is applied to one side thereof in accordance with a predetermined pattern. Then, the web is cut into tip-paper pieces. Each tip-paper piece is supplied to the rolling section, where the tip-paper piece is rolled around two cigarettes with a filter-plug between, in the manner that the tip-paper piece covers the filter-plug and one end of each cigarette. Then, glue is dried.
In the present invention, since the water-content of a tip-paper piece is, in advance, stabilized in an absolute dry region, i.e., a lower water-content region as compared with a normal water-content region, variation of the water-content of a tip paper piece which happens when glue is dried after the tip-paper piece is rolled is stable, that is, not very different between tip-paper pieces. Thus, the shrinkage percentage of a tip-paper piece is stable, that is, it is in a limited range. Thus, the space between the circumference of a filter-tip and a tip-paper piece does not vary irregularly between products. When products are made to have the same circumferential tip space, difference in air-flow resistance in holes between products is restricted. Thus, the ratio of the air flowing into a filter is stabilized.
In the present invention, web drying means may comprise a heater for heating a web, which is arranged halfway on a web feed path, and a control unit for controlling heating temperature at which the heater heats. In this case, when a web is drawn out, the heater heats the web, which passes the heater touching a heating surface thereof, to thereby lower the water content of the web into an absolute dry region. The control unit decides the amount of heat required to lower the water content of a web into an absolute dry region only by the heating surface of the heater touching the traveling web, and controls the heating temperature at which the heater heats. Here, it is to be noted that the heater is only an example. The drying means is not restricted to a heater.
In order to lower the water content of a web into an absolute dry region, it is desirable that the heater""s heating temperature is controlled in a temperature region of 200xc2x0 C. and above. In this case, when a web is drawn out in an actual filter attachment machine, the heater gives heat enough to preliminarily dry the web.
The heater""s heating temperature can be varied taking account of the speed at which a tip-paper web travels. Specifically, when a tip-paper web travels at lower speed, the heater""s heating temperature is set at lower temperature. Conversely, when a tip-paper web travels at higher speed, the heater""s heating temperature is set at higher temperature. To sum up, what is needed is that heat enough to lower the water content of a travelling web into an absolute dry region is transferred from the heater. The heater""s heating temperature does not always need to be 200xc2x0 C. or higher.
When the present invention further comprises means for making the heater and a web approach or recede from each other, it is possible to make space between the heating surface of the heater and a web when the web, which has been being drawn out, is stopped, to thereby keep the web from being damaged by overheating.
In a desirable mode of the present invention, the drying means further comprises a water-content sensor for detecting the water content of a web, at least at one position which is behind or ahead of the heater, and sending out a detection signal. The control unit controls the heater""s heating temperature on the basis of a detection signal from the water-content sensor. In this case, the heating temperature is controlled dynamically, depending on the detected water-content of a web. This makes the water content after drying more stable.
In the case where the water-content sensor detects the water content of a web at a position behind the heater, the heater""s heating temperature is controlled in the form of proportional control (open loop) on the basis of a detection signal from the water-content sensor. The control unit calculates the amount of heat required for drying a web on the basis of the detected water content proportionally, and decides the heater""s heating temperature.
In the case where the water-content sensor detects the water content of a web at a position ahead of the heater, the heater""s heating temperature is controlled in the form of feedback control on the basis of a detection signal from the water-content sensor. The control unit corrects, i.e., raises or lowers the heater""s heating temperature so that the detected water content may be in a dry region. In the case where the water content of a web is detected both at a position behind the heater and at a position ahead of the heater, the control unit can perform both proportional control and feedback control on the basis of two detection signals. It is to be noted that in the present invention, it is not always necessary to use the control unit and water sensor.
For example, the absolute dry region may be defined as a water-content region of 4% and below in terms of the water-content of a tip-paper piece, depending on environmental conditions of a country or a region. Let us suppose that a web is preliminarily dried by the apparatus for stabilizing air permeability characteristic according to the present invention. In that case, a web which had a higher water content before drying has its water content lowered to a larger degree. A web which had a lower water content before drying has its water content lowered to a smaller degree. Thus, when the water content of a web is lowered into a water-content region of 4% and below by preliminary drying, the web as a whole has a compressed, narrow range of water content as compared with the range of water content before drying. This means that the water-content of a web is stable in a region of 4% and below. Further, when, in the filter attachment machine, a tip-paper piece is rolled and then glue is dried (this is not preliminary drying), the influence of variation of the water content of the tip-paper piece upon the shrinkage percentage thereof is larger in the case where the tip-paper piece had a higher water content before drying, and smaller in the case where the tip-paper piece had a lower water content before drying. Thus, when the water content of a web is lowered into a low water-content region of 4% and below prior to rolling of tip-paper pieces, the range of shrinkage percentage which the tip-paper pieces show after rolling is compressed and narrowed. Thus, products have stable circumferential tip space. It is to be noted that this does not mean that in all countries and regions, the water content of a web needs to be lowered into a water-content region of 4% and below. The absolute dry region should be defined depending on environmental conditions of a country or region where the present invention is carried out.